Structural characteristics of the Inter Tropical Convergence Zone over the equatorial Indian Ocean during INDOEX-1999 field phase experiment

Inter Tropical Convergence Zone (ITCZ) is a narrow region (of about 200-300 km in width) where trade winds emanating from different hemispheres (northern/ southern) converge. In an averaged sense around the globe, ITCZ lies to the north of the equator during the northern summer and to the south of the equator during the northern winter/southern summer. Typical patterns of the ITCZ are examined for the active and weak phases of its activity through the evaluation of meridional plane divergent circulation, temperature and moisture, etc. In an attempt to study the performance evaluation of the global data assimilation and forecasting system (GDAFS) in predicting the enhanced ITCZ activity, the successive day-3 forecasts are utilized to delineate the predictive characteristics associated with the ITCZ over the equatorial Indian Ocean. Further, the assessment of the impact of INDOEX glass sonde data on the analysis circulation over the equatorial western Indian Ocean with regard to the cyclonic circulation formed around 5 February 1999 is attempted. It is found that the operational analyses brings out the active and weak phases of the ITCZ activity over the equatorial Indian Ocean quite well, Further, the successive day-3 forecasts of the GDAFS are found to be reasonably successful in predicting the typical enhancement of the ITCZ activity. Assimilation of the INDOEX glass sonde data for a selected period suggests a general improvement in the description of the cyclonic circulation and its associated characteristics.